In general, vehicle power transmission apparatus generally uses so-called multiple disk clutches to arbitrarily transmit or cut off power of an engine to or from the vehicle wheels. In such a power transmitting apparatus, it has an input member connected to an engine side, an output member connected to a driven side, and a clutch member connected to the output member. The power can be transmitted by pressure-contacting a plurality of driving clutch plates mounted on the input member and a plurality of driven clutch plates mounted on the clutch member. The power can be cut off by releasing the pressure-contacting force between the driving and driven clutch plates.
The prior art (e.g. European Laid-open Patent Specification No. 1058018) discloses technology which provides cams to add a pressure-contact assist function to improve the pressure-contacting force of both the driving and driven clutch plates during power transmission. Also, they provide a back-torque limiting function to release the clutch plates of the input and output sides when the rotation speed of the output member has exceeded that of the input member. According to this power transmitting apparatus, two cams are formed with gradients on each engaging surface of a clutch housing and a driving clutch plate. Thus, both the driving and driven clutch plates are strongly pressure-contacted by one pair of cams (pressure-contact assist cams) during the normal power transmission. On the contrary, the driving clutch plates are moved by the other pair of cams (back-torque limiting cams) toward a direction where the pressure-contact between the driving and driven clutch plates is released when back-torque is present.
However in the power transmitting apparatus of the prior art, since the pressure contact assist cams and back-torque limiting cams are formed on engaging surfaces between a clutch housing and driving clutch plates, with a gradient angle, the strength of the cams is sometimes insufficient.
Accordingly, to overcome this disadvantage, the applicant of the present invention provides the pressure contact assist cams and back-torque limiting cams on recesses of the clutch member and stopper portions on the pressure plate. All are made of high strength material to be used to prevent relative rotation between the clutch member and the pressure plate.
The stopper portions project from and are formed integrally with the pressure plate. The stopper portions are adapted to fit into recesses formed on the inner circumferential surface of the clutch member. This fit prevents relative rotation between the pressure plate and the clutch member. Thus, both the clutch member and the pressure plate are made of material having high strength. Therefore, the integrally formed pressure contact assist cams and back-torque limiting cams also have high strength to perform a function as a cam. In general, since the clutch member and the pressure plate are formed by casting, two cams, the pressure contact assist cam and back-torque limiting cam are formed in accordance with a profiled surface of preformed dies.
However, in the power transmitting apparatus mentioned above, since the gradient surfaces are formed on the stopper portion of the pressure plate and the recess of the clutch member which are formed by casting, a problem exists that either one of the pressure contact assist cams and/or back-torque limiting cam becomes a reverse draft surface. Thus, casting of them becomes difficult.
Ordinarily, casting is carried out by pouring molten metal into a cavity which is formed between movable dies and stationary dies with profiled surfaces corresponding to a configuration of an article to be cast. However, either one of the pressure contact assist cam and back-torque limiting cam is molded to a configuration (such a configuration is called as a “reverse-draft surface”) which inevitably interferes with the profiled surface of the movable die when separating the movable die from the stationary die after molding. This makes the molding of the pressure-contact assist cam and back-torque limiting cam difficult.